BOSTON, Massachusetts (CNN) -- Vowing to change the direction of the country and "write the next great chapter of America's history," Sen. John Kerry of Massachusetts accepted the Democratic presidential nomination before cheering delegates at Boston's FleetCenter.

"I'm John Kerry, and I'm reporting for duty," the Massachusetts senator said Thursday night while saluting the cheering crowd of Democratic delegates that packed Boston's FleetCenter.

Kerry's speech, in which he accepted his party's presidential nomination, focused mainly on the economy and the war in Iraq. (Key points)

Kerry called the coming presidential contest "the most important election of our lifetime."

"America can do better, and help is on the way," he said repeatedly.

In an attempt to appeal to middle-class workers, he said that "wages are falling, health care costs are rising" under the Bush administration, and then promised steps to reverse that.

"I will cut middle class taxes. I will reduce the tax burden on small business. And I will roll back the tax cuts for the wealthiest individuals, who make over $200,000 a year, so we can invest in job creation, health care and education."

He also vowed to neither privatize Social Security nor cut the benefits.

But with polls showing Americans have more trust in President Bush than Kerry on national security matters, defense and security made up much of Kerry's speech.

"I defended this country as a young man, and I will defend it as president," he said after being introduced by former Sen. Max Cleland of Georgia, a fellow Vietnam veteran, who lost both legs and an arm in the war.

"I will never hesitate to use force when it is required. Any attack will be met with a swift and certain response," Kerry vowed. "I will never give any nation or international institution a veto over our national security.

"I will be a commander in chief who will never mislead us into war."

Kerry said that by building a stronger military and stronger alliances around the world, America will be able to tell terrorists: "You will lose and we will win."

He also said he would add more active duty troops and "end the backdoor draft of National Guard and reservists," referring to the extended tours those troops are serving.

Kerry's address -- the finale of the convention -- was enthusiastically received by the delegates, who interrupted him with more than two dozen standing ovations.

"I called my wife back home and told her, 'I think we found a president,'" said Michael Najarian, a delegate from Binghamton, New York.

Carol Summerlyn, a delegate from Portsmouth, Virginia, pronounced it "fantastic."

"I think it's clear we're all unified," she said. "This country is going to change."

On Friday, Kerry and running mate Sen. John Edwards will embark on a two-week, 21-state, coast-to-coast campaign journey that will begin with stops in three key battleground states -- Pennsylvania, West Virginia and Ohio. The Democratic National Committee will also launch a new ad campaign on their behalf.

Answering critics

In his speech, Kerry said his opponents should not call him a pessimist for offering new ideas. He also said the Republicans do not have a monopoly on the flag and patriotism.

Kerry, a Catholic, declared that though he doesn't wear his faith on his sleeve, it has shaped his life.

"I don't want to claim that God is on our side. As Abraham Lincoln told us, I want to pray humbly that we are on God's side."

In critiquing Kerry's speech, Terry Neal of WashingtonPost.com said the often stiff-appearing Kerry looked "like a normal guy."

"I thought his delivery was almost as effective as the message," Neal said.

Joe Klein of Time magazine described Kerry's "call for civility and unity in the campaign" as a gauntlet thrown down to President Bush, who has "put his name on about $80 million in negative ads."

But CNN's Jeff Greenfield was surprised by something that was almost missing in Kerry's speech.

"I really have never heard an acceptance speech where 20 years of a guy's life in the U.S. Senate is kissed off in three sentences," Greenfield said.

Kerry and running mate John Edwards acknowledge cheering delegates as the convention ends.

Those three sentences were:

"When I came to the Senate, I broke with many in my own party to vote for a balanced budget, because I thought it was the right thing to do. I fought to put 100,000 cops on the street," Kerry said.

"And then I reached across the aisle to work with John McCain, to find the truth about our POWs and missing in action, and to finally make peace with Vietnam."

Surrounded by veterans and family

It was a family affair for Kerry in his hometown.

His "band of brothers," crewmates on his swift boat in Vietnam, spoke of his courage in battle.

Jim Rassmann, a soldier who served with Kerry, said he wasn't asked to appear at the convention Thursday night, rather, he volunteered. He said it wasn't because Kerry saved his life during the war, but because he had witnessed Kerry's "bravery and leadership under fire."

"Any one of these 12 guys will tell you, in a tight situation, when your whole future -- your whole life -- depends on the decisions of one man, you can count on John Kerry," Rassmann said.

Kerry's two daughters, Vanessa and Alexandra, and his stepson Andre Heinz, spoke of the qualities the four-term senator possesses that they said will make him a good president.

They also introduced a biographical film on the Democratic presidential nominee, narrated by actor Morgan Freeman and made with the advice of Steven Spielberg.

The convention theme "Stronger at Home, Respected in the World," was stressed in speeches from foreign policy experts, including former presidential hopeful and NATO Supreme Commander Gen. Wesley Clark, and Sen. Joseph Biden of Delaware, the ranking member on the Senate Foreign Relations Committee. (Special Report: America Votes 2004)

Biden said he believed history would judge the Bush administration "harshly for the mistakes it has made" and opportunities it has "squandered" by not enlisting the help of U.S. allies.

Clark said he respected Kerry as a fellow soldier who went to war and as a veteran who returned home to fight for peace.

He also warned delegates, "Anyone who tells you that one political party has a monopoly on the best defense of our nation is committing a fraud on the American people." (Full story)

Former Secretary of State Madeleine Albright said Kerry would "use intelligence to shape policy, not twist intelligence to justify policy."

Other developments

Analysts predict a convention bounce for Kerry but say this week represents just one step in a long campaign -- and that a lot can happen before November. (Full story)

Protesters outside the Democratic National Convention skirmished briefly with police Thursday. Police reported four arrests, but not all were related to that clash. (Full story)

After lying low during the Democratic convention, President Bush will go back on the campaign trail Friday, unveiling the broad themes of his agenda for the next four years at stops in Missouri, Michigan and Ohio, all crucial battleground states, a senior aide told CNN. (Full story)